Method for Drilling Oil and Gas Wells

ABSTRACT

When drilling or completing an oil or gas well, it is often desirable to drill a borehole at an angle to the initial borehole. A process for deflecting a well tool towards the wall of a well bore comprises positioning within the well bore a radially expandable pipe designed to curve longitudinally when its diameter is expanded, expanding the diameter of the radially expandable pipe thereby causing the pipe to curve and passing the well tool through the curved pipe: The process is particularly suitable for through-tubing operations in which a lateral bore is initiated from a production well having within the well a smaller diameter production tubing ( 14 ) comprising (i) passing through the production tube ( 14 ) a radially expandable pipe ( 1 ) designed to curve longitudinally as its diameter is expanded, into a section of well bore ( 12 ) having a diameter greater than the diameter of the production tubing ( 14 ) (ii) expanding the diameter of the radially expandable pipe ( 1 ) thereby causing the pipe to curve, (iii) passing through the curved pipe a milling device or drill bit and (iv) milling the casing or drilling into the well bore wall.

The present invention relates to a method and apparatus for drilling oil and gas wells. In particular, the invention relates to a method and apparatus for opening a window in a well bore to initiate a lateral well bore and for drilling a well bore through such a window.

When drilling or completing an oil or gas well, it is often desirable to drill a borehole at an angle to the initial, substantially vertical, borehole. For example, it may be necessary to establish a new drilling course for directional or horizontal drilling, or it may be necessary to sidetrack the original borehole to avoid a section of damaged bore, junk in the hole, or other negative well conditions.

In order to initiate or “kick-off” a deviated well, it is necessary to deflect the drilling tool through the wall of the initial well bore. A deflecting tool known as a “whipstock” has been known and used for many years to achieve the deflection of the drilling tool. Whipstocks can be used in both cased and open hole. Where the initial well bore is cased, a window is first milled in the casing and then the drilling tool is deflected through the window to drill the lateral well. Although other methods, such as the use of bent subs and mud motors have been developed, whipstocks are still widely used to deflect the milling and drilling tools to kick-off lateral wells. Some whipstock designs are intended to be left downhole, whereas others are designed to be retrieved.

The standard whipstock is generally an elongate tool, typically about 3 m to 6 m long, which has the general cross-sectional shape of a right triangle. The short base of the right triangle is the bottom of the whipstock in the well bore. An upstanding back surface intersects the base at essentially a right angle. The hypotenuse is the gently sloping guide surface of the whipstock which is designed to direct the well tools into a direction which is at an angle to the longitudinal axis of the initial well bore.

To be effective, the whipstock must be positioned and secured in the well bore at the required location and orientation. A whipstock can be set on the bottom of the initial well bore, or on top of a suitable anchor or cement plug. Some designs of whipstock may be used in the open hole. The upstanding back surface of the whipstock may rest on the wall of the well bore or the casing lining the well bore. When secured in this manner the whipstock provides a stable platform for guiding the mill or drilling tool.

A common problem with known whipstocks is that the starter mill or drill can damage the whipstock, adversely affecting the drilling of the lateral. In some cases the attempt to drill the lateral may have to be abandoned and begun again at a different, usually higher, location in the initial well bore. This will entail significant cost and loss of time.

Sometimes the interior of the initial well bore has one or more restrictions along its length that reduce the cross-sectional area of the wellbore. For example, the well bore may have a string of production tubing that is carried concentrically within the main wellbore and that is of a smaller internal diameter than the wellbore or any casing lining the wellbore. Typically, the wellbore has an internal diameter of about 5 inches (12.7 cm) to about 10 inches (25.4 cm), for example 7 inches (17.8 cm) and the production tubing has an internal diameter of about 2.5 inches (6.4 cm) to about 6 inches (15.2 cm), for example 4.5 inches (11.4 cm). This means that any tool that is passed down the interior of that well bore, including a whipstock, has to be small enough in cross-section to pass through the restriction in order to reach lower levels in the wellbore. This is called through-tubing operations in that any well operations that are to be carried out in the well bore below the end of the production tubing require the equipment to be passed through the interior of the production tubing before it can reach the area where the well operation is to be carried out. The alternative would be to remove the production tubing in its entirety from the well bore, which is an expensive and time consuming process. Thus, it is very desirable to be able to pass well tools that are to be used in well operations through the interior of the smaller diameter production tubing down below the end of that tubing into the larger diameter wellbore and then carrying out well operations with those tools in that larger area of the wellbore.

Unfortunately, some tools that are made small enough to pass through restrictions such as production tubing do not operate as well in the larger diameter well bore area below the end of the production tubing and this includes whipstocks. This is because the small tools do not adequately take up the space afforded by the larger well bore area. In particular, the upstanding back surface of the whipstock may not be adequately supported. Some through-tubing whipstocks are set diagonally across the larger diameter bore hole and so only the top section rather than substantially the full length of the back surface is in contact with the wall or casing opposite the wall in which the window is to be milled and the bottom of the guide surface of the whipstock is positioned against the wall into which the window is to be milled. In this position, the whipstock may flex or bend when contacted by the milling or drilling tools, which can result in the mill or drill jumping off the guide surface of a whipstock. Some designs of whipstock have hinged sections that can be opened after the whipstock has been passed through the restriction to provide improved support for the whipstock. However, these more complex devices may still provide insufficient guidance to the milling and drilling tools. Sometimes the through-tubing whipstock can slip within the hole and as a result may provide inadequate guidance to the milling and drilling tools.

The present invention relates to an alternative method of initiating or drilling a lateral well and more specifically to a method that can be used in the larger diameter area of a well bore below the end of a restriction through which the tools must pass.

The term “side track well” is sometimes used to describe a branch from an existing wellbore where the existing wellbore no longer produces hydrocarbon fluid and the term “lateral well” is sometimes used to describe a branch from an existing wellbore where the existing wellbore continues to produce hydrocarbon fluid. The present invention can be used in any wellbore from which a second, branched, wellbore is to be drilled. References herein to lateral wells or bores should be understood to include any such wells, whether or not the existing well continues to produce. Indeed, should the need arise; the invention could be used to drill a lateral well in an injection well.

Thus, according to the present invention, a process for deflecting a well tool towards the wall of a well bore comprises positioning within the well bore a radially expandable pipe designed to curve longitudinally when its diameter is expanded, expanding the diameter of the radially expandable pipe thereby causing the pipe to curve and passing the well tool through the curved pipe.

The present invention is particularly suitable for through-tubing operations and includes a process for initiating a lateral bore from a production well having within the well a smaller diameter production tubing comprising (i) passing through the production tube a radially expandable pipe designed to curve longitudinally as its diameter is expanded, into a section of well bore having a diameter greater than the diameter of the production tubing (ii) expanding the diameter of the radially expandable pipe thereby causing the pipe to curve, (iii) passing through the curved pipe a milling device or drill bit and (iv) milling the casing or drilling into the well bore wall.

The milling device or drill bit may be attached to the lower end of a drill string or may be used at the end of a wireline. The present invention can be used with remotely controlled drilling devices. Such devices are known. For example, U.S. Pat. No. 6,305,469 and PCT Patent Application WO 2004/011766 disclose methods for drilling a wellbore using a remotely controlled drilling device. By controlling stabilisers for the remotely controlled drilling device, the drill bit can be tilted in the wellbore to start drilling a curved wellbore section. The drilling device may be provided with a remotely operable steering means, for example, a steerable joint, which can be used to adjust the trajectory of the new wellbore section as it is drilled.

The present invention includes a radially expandable pipe for use in the process, which has over at least part of its length an asymmetrical wall thickness.

The asymmetrical wall thickness can be provided by any known method. For example, the pipe may be manufactured by rolling or extrusion such that the wall thickness is not symmetrical over at least a portion of the pipe. The asymmetry may be provided by machining the internal or external surfaces of a pipe that initially has a substantially uniform wall thickness. Suitable material may also be fixed to the external surface of the pipe to provide a thicker wall.

The radially expandable pipe is generally made of steel and any material fixed to the outer surface is also preferably steel. Suitably, the pipe comprises a steel pipe of substantially uniform wall thickness and at least one length of steel is securely attached to the outer surface of the steel pipe. Conveniently, the length of steel may be attached to the pipe by welding around all or part of its periphery. The length of steel may be of any shape but preferably comprises a cylindrical section having an internal surface which is an arc of a circle having a central angle of from about 2 to about 160 degrees, typically from about 2 to about 20 degrees or 5 to about 20 degrees, and a radius which is substantially the same as, or slightly larger than, the external radius of the pipe. The length of steel attached to the pipe may be of substantially uniform thickness. In this case, there will be a step change in the wall thickness. It is preferable that the wall thickness gradually increases and decreases around the pipe. The length of steel welded to the pipe may therefore preferably be crescent shaped in cross-section.

The asymmetric wall thickness may extend along the whole length of the pipe or only a part of the length.

The relative thicknesses of the wall of the pipe and the length of the asymmetry are selected to achieve the desired curvature in the pipe as it is expanded. Since the pipe is to be curved down the well bore, it must be designed such that expanding the pipe to the desired internal diameter results in the desired curvature without exerting unacceptable stresses on the well bore. For example, in an uncased wellbore, it may be undesirable if the expansion would result in a greater curvature of the pipe, but for the limitations of space in the well bore, resulting in the walls of the well bore being put under compressive stress, as this could result in damage to the formation.

The person skilled in the art could readily determine the design of the pipe that will provide the appropriate curvature on expansion of the pipe. This may require some trials with pipe of the size and material to be used. When drilling a deviated well, the amount of deviation from the vertical may typically be of the order of 1 or 2 inches (2.54 to 5.08 cm) per 10 feet (3 m) of depth, i.e. the angle of deviation of the lateral bore may be of the order of about 0.4 to about 1.0 degree although greater or smaller deviations may be used in some applications.

Expandable pipe for use in oil and gas wells is known. For example, it is known to position pipe downhole and then expand it. This technology is used, for example, in producing monobore casing or production tubing where a tubing string of smaller diameter is lowered through wider diameter tubing and then expanded to substantially the same diameter as the wider diameter tubing.

Any of the known methods for expanding pipe may be used in the present invention such as by urging a mandrel or conical expander through the pipe or using a system of rolling the pipe using balls or rollers, which are urged outwardly against and rotated around the inner surface of the pipe. An example of the latter type of expanding apparatus is disclosed in US Patent Application Publication US 2001/0045284. When a pipe is expanded using a mandrel forced through the pipe, the diameter of the pipe may be typically increased by about 10 to 20% and the overall length reduces by about 5%. Whereas, when the expansion is achieved using rotating balls or rollers, an expansion of about 10 to 20% in diameter is accompanied by an increase in the overall length of the pipe of about 5%.

Due to the asymmetric wall thickness of the expandable pipe the pipe expands preferentially where it is less thick. This causes the pipe to become curved.

The expandable pipe may be oriented before or after expansion, but is preferably oriented before expansion. Known techniques can be used to orient the pipe within the well bore so that after expansion the curved pipe will direct the well tools in the desired direction.

Preferably spacers are used to support the curved pipe in the well bore. Spacers are therefore preferably positioned around the circumference and along the length of the curved pipe. Suitable spacers are known and include, for example, bow spring centralizers.

The upper end of the curved pipe is preferably centralised and held securely within the well bore. Suitable spacers to achieve this would be substantially cylindrical and expand substantially symmetrically around the circumference of the pipe. However, in order to support the curved pipe in the substantially straight hole, the supports along the length of the curved pipe will have to bridge a wider gap at one side of the curved pipe than at the other. Thus, the radially expandable pipe preferably has spacers that are designed to expand asymmetrically about the centre of the pipe. This could be for example, a substantially cylindrical spacer having elements that are designed to expand asymmetrically about the centre of the pipe. The invention includes a radially expandable pipe having a plurality of spacers positioned along the length and around the circumference of the radially expandable pipe such that when the pipe is expanded the spacers expand to different radial lengths to hold the curved pipe in place within the well bore.

The invention includes a radially expandable pipe having at least one spacer positioned along its length the spacer comprising a deformable elongate member having a first end and a second end, each of said ends being attached to the radially expandable pipe such that as the pipe is expanded the change in the length of the pipe deforms the elongate member so that it projects radially from the centre of the pipe. The amount of radial expansion required for the spacer will depend on the location in which it is to be used. An expansion of up to and in some cases exceeding 80% of the initial radial length may be desired for the spacer. For example, in order to be capable of passing through a 4.5 inch (11.4 cm) internal diameter production tubing, the radial length of the radially expandable pipe and spacer would be about 2 inches (5 cm) and in order to support the pipe in a 7 inch (17.8 cm) internal diameter casing, the expanded radial length would be about 3.5 inches (8.9 cm); an expansion of about 75% of the original radial length.

The outer surface of the spacer may be provided with means to improve the grip with the casing or wellbore wall after expansion. For example, the outer surface may be shaped, coated or treated to provide a rough surface. A suitable surface can be provided by thermally spraying the surface with a metal carbide.

The deformable elongate member can be a bow spring attached at each end such that a reduction in the length of the pipe, such as occurs when the pipe is expanded using a mandrel, forces the ends towards each other and the bow spring bows outwardly. The bow spring can initially lie substantially flat against the surface of the pipe. This facilitates movement of the expandable pipe down the well and into position. Expansion of the pipe causes the bow spring to expand and engage the wall of the well bore or the casing of the well.

Preferably, the spacer comprises a plurality of bow springs arranged around the circumference of the radially expandable pipe. The bow springs can be attached together at the ends to form a substantially cylindrical cage structure. By selecting different shapes, lengths, thicknesses and/or materials, the bow springs can be made to bow more or less for the same reduction in length of the expandable pipe. The bow spring must be made of material and designed to provide sufficient stiffness to provide support for the expanded pipe.

In another embodiment, the deformable elongate member can be an articulated element, each end of which is attached to the expandable pipe such that an increase in the length of the pipe, such as occurs when the pipe is expanded using a rolling ball or roller expander, causes the ends of the deformable elongate member to move away from each other and the articulated member moves from a first position close to the surface of the expandable pipe to a second position which is radially extended from the centre of the pipe. For example, the articulated element may be a folded element that is a single piece of material folded to form the folded element. Another embodiment of the articulated element comprises two or more pieces of material fixed together to form the articulated element. The articulated element may have a joint towards one or both ends and/or along its length. An example of a suitable articulated element comprises a length of material folded into two unequal legs and attached by the end of each leg to the expandable pipe such that in cross-section, the external wall of the pipe and the two legs of the deformable elongate member have the form of an obtuse triangle. The obtuse angle is preferably greater than 120 degrees in order that in the first position, the articulated element lies close to the wall of the pipe. A similar articulated element comprises two lengths of material fixed together at one end and the other ends are attached to the pipe.

A person skilled in the art will readily be able to select or design one or more spacers that will support the curved pipe in the well bore.

The process according to the present invention is particularly suitable where it is necessary to pass the well tools required to initiate and drill a lateral well through the interior of a smaller diameter production tubing down below the end of that tubing into the larger diameter well bore and then carrying out the initiation or drilling of the lateral well with those tools in that larger area of the well bore. The radially expandable pipe is lowered down the well bore, through the smaller diameter production tubing and down into a cased or open hole of greater diameter. The radially expandable pipe can be centralised within the larger diameter well bore, using suitable centralising equipment. Means for expanding the radially expandable pipe are introduced into the interior of the pipe and the pipe expanded. The pipe can conveniently be expanded to substantially the same as the internal diameter of the last section of the production tubing. As it expands, the asymmetric wall thickness causes the pipe to curve. Spacers can be provided to support the pipe within the well bore. These can be of the type described above that are fixed to the pipe and are deployed as the pipe is expanded. Optionally, the spacers initially support the pipe centrally, but are distorted as the pipe expands and curves.

In an embodiment of the invention, a window is first milled in the casing and then the radially expandable pipe is lowered into position adjacent the window and then expanded and curved such that the window provides more space to accommodate the curved pipe. A suitable method for forming a window in the production tube or casing is disclosed in PCT Patent Application WO 2004/046499. The disclosed method of cutting a window in a tubular, in particular a casing, comprises using a remotely controlled electrically powered cutting tool that has a pivotally mounted cutting head that can be pivoted towards the wall of the tubular.

The invention will now be described with reference to the accompanying drawings in which:

FIG. 1 is an isometric drawing of part of a radially expandable pipe suitable for use in the present invention.

FIG. 2 is a cross-sectional drawing of the expandable pipe of FIG. 1 taken through A-A.

FIG. 3 is a cross-sectional drawing of another embodiment of a radially expandable pipe suitable for use in the present invention.

FIG. 4 is a schematic sectional drawing of the radially expandable pipe being expanded and curved by an expanding device.

FIG. 5 is a schematic sectional drawing of a bow spring spacer before expansion of the radially expandable pipe.

FIG. 6 is a schematic sectional drawing of the bow spring spacer of FIG. 5 after expansion of the radially expandable pipe.

FIG. 7 is a schematic sectional drawing of a folded spacer before expansion of the radially expandable pipe.

FIG. 8 is a schematic sectional drawing of the folded spacer of FIG. 7 after expansion of the radially expandable pipe.

FIG. 9 is a schematic sectional drawing of an alternative articulated spacer before expansion of the radially expandable pipe.

FIG. 10 is a schematic sectional drawing of the alternative articulated spacer of FIG. 9 after expansion of the radially expandable pipe. FIG. 10 a illustrates an expanded cross-section of the spacer showing a profile of the legs 9 and 10.

FIG. 11 is an illustration of an expanded pipe in place in the well bore.

FIGS. 1 and 2 illustrate part of a radially expandable pipe 1 which has, over at least part of its length, an asymmetrical wall thickness. The asymmetrical wall thickness is provided by securely fixing to the outside surface 4 of the pipe a length of steel 2. The length of steel 2 comprises a cylindrical section having an internal surface that is an arc of a circle having a central angle θ of about 90° and a radius which is substantially the same as the external radius of the pipe. The length of steel 2 is fixed to the pipe by welding along the outer edges 3, that are transverse to the longitudinal axis of the expandable pipe 4. Thus the length of steel 2 is not welded along the longitudinal edges 5.

FIG. 3 is a cross section of an alternative radially expandable pipe in which the asymmetrical wall thickness is provided by the inner surface 6 and outer surface 4 being eccentric.

FIG. 4 is a schematic drawing of an expandable pipe 1 in which, as for FIG. 1, the asymmetrical wall thickness is provided by a length of steel 2 securely fixed to the outer surface 4 of the pipe by welding along the outer edges 3. The pipe has been expanded and curved by the action of an expanding device 16. The expanding device can be any suitable expanding device such as a mandrel expander or a ball or roller type expander as shown, for example, in US Patent Application Publication US 2001/0045284.

FIGS. 5 to 10 are schematic sectional drawings illustrating spacers that could be used in the present invention.

FIGS. 5 and 6 show a spacer 7 comprising a length of material fixed at each end to the radially expandable pipe 4. The spacer is designed to act like a bow spring. In the first position shown in FIG. 5, the spacer lies alongside the outer surface 4 of the expandable pipe. As the radially expandable pipe 4 is expanded, for example by pulling a mandrel through the pipe, the axial length of the pipe decreases; the fixed ends of the bow spring 7 move towards each other causing the spring to bow and extend radially from the pipe surface as shown in FIG. 6.

FIGS. 7 and 8 show a folded spacer 8 fixed to the outer surface 4 of a radially expandable pipe. The folded spacer is folded at each end and, as shown in FIG. 7, initially lies in a first position alongside the outer surface 4 of the expandable pipe. Expansion of the radially expandable pipe 4, for example by using a rolling ball or roller expander, causes the fixed ends of the folded spacer 8 to move away from each other and the spacer is unfolded such that it extends radially from the surface of the expandable pipe, as shown in FIG. 8.

FIGS. 9 and 10 show another embodiment of an articulated spacer, which comprises two legs 9 and 10. The two legs are of unequal length and could have been formed by folding a single piece of material, but as shown more clearly in FIG. 10 the spacer comprises two, initially separate, pieces of material joined, e.g. by welding at one end 11. The other ends of the legs are fixed to the surface of the radially expandable pipe 4. As shown in FIG. 9, the spacer comprising the two legs 9 and 10 initially lies in a first position alongside the outer surface 4 of the expandable pipe. Expansion of the radially expandable pipe 4 causes the fixed ends of the spacer to move away from each other and the spacer unfolds such that it extends radially from the surface of the expandable pipe, as shown in FIG. 10. FIG. 10 a shows the profile of the legs 9 and 10 taken along B-B of FIG. 10. Such a profile can provide additional stiffness to the spacers as compared with flat substantially rectangular sections. When the spacer is lying adjacent the surface of the radially expandable pipe 4 as shown in FIG. 9, the two legs 9 and 10 and the surface of the pipe form an obtuse triangle with the obtuse angle being about 170 degrees. When the spacer is extended, the triangle is still obtuse, but the obtuse angle is shown as about 100 degrees.

It will be appreciated that if identical spacers are placed around the circumference of the pipe at about the same axial position and are subjected to the same change in the length of the expandable pipe 4, then the spacers will be displaced from the surface 4 of the expandable pipe by substantially the same amount and the arrangement will tend to centralise the expandable pipe. By using different spacers, e.g. spacers of different lengths then they will be deflected from the surface 4 of the expandable pipe by different amounts and the spacers will provide asymmetric support.

FIG. 11 illustrates a curved expanded pipe 1 in the cased well bore 12. As the curved expanded pipe 1 is wider than the cased well bore 12, it is apparent that the window 13 was milled through the casing 12 and into the formation before the radially expandable pipe 1 was expanded and curved. This could be achieved, for example, by using the apparatus and method disclosed in PCT Patent Application WO 2004/046499. After milling the window 13, the radially expandable pipe 1 was passed down the well bore and through the production tube 14. It was centralised in the well bore using centraliser 15. The radially expandable pipe was then expanded to substantially the same internal diameter of the production tube 14. Due to the asymmetric wall thickness of the radially expandable pipe in the region 17, expansion of the pipe caused it to bend at 18. The lower end of the pipe passed through the window 13. As the pipe expanded, the spacers 19 fixed to the surface of the pipe extended to support the curved pipe in the well bore. 

1-13. (canceled)
 14. A process for deflecting a well tool towards the wall of a well bore comprising positioning within the well bore a radially expandable pipe designed to curve longitudinally when its diameter is expanded, expanding the diameter of the radially expandable pipe thereby causing the pipe to curve and passing the well tool through the curved pipe.
 15. A process as claimed in claim 14 in which a lateral well bore is initiated from a production well having within the well bore a smaller diameter production tubing comprising (i) passing through the production tube a radially expandable pipe designed to curve longitudinally as its diameter is expanded, into a section of well bore having a diameter greater than the diameter of the production tubing, (ii) expanding the diameter of the radially expandable pipe thereby causing the pipe to curve, (iii) passing through the curved pipe a milling device or a drill bit and (iv) milling the casing or drilling into the well bore wall.
 16. A process as claimed in claim 15 in which a lateral well bore is initiated from a cased production well having within the well bore a smaller diameter production tubing comprising (i) milling a window in the casing of the well bore, (ii) passing through the production tube a radially expandable pipe designed to curve longitudinally as its diameter is expanded, into a section of well bore having a diameter greater than the diameter of the production tubing, (iii) orienting the radially expandable pipe within the well bore, (iv) expanding the diameter of the radially expandable pipe thereby causing the pipe to curve into the milled window, (v) passing through the curved pipe a drill bit and (vi) drilling into the well bore wall.
 17. A process as claimed in claim 14 or claim 15 in which the radially expandable pipe is oriented within the well bore prior to expansion.
 18. A process as claimed in claim 14 or claim 15 in which at least one spacer is used to support the curved tube within the well bore.
 19. A process as claimed in claim 15 in which the angle of deviation of the lateral bore is from about 0.4 to about 1.0 degree.
 20. A radially expandable pipe for use in the process as claimed in claim 14 or claim 15 which has over at least part of its length in asymmetrical wall thickness.
 21. A radially expandable pipe as claimed in claim 20 in which the asymmetrical wall thickness is provided by securely fixing a length of steel longitudinally on the outer surface of a cylindrical pipe.
 22. A radially expandable pipe as claimed in claim 20 in which the length of steel comprises a cylindrical section having an internal surface which is an arc of a circle having a central angle of from 2 to 20 degrees and a radius which is the same as or slightly larger than the external radius of the pipe.
 23. A radially expandable pipe having at least one spacer fixed to the outer surface, the spacer comprising an elongate element having a first and second end each of which is securely fixed to the pipe such that the change in length as the pipe is expanded deforms the elongate element, increasing its maximum radial distance from the centre of the pipe.
 24. A radially expandable pipe as claimed in claim 23 in which the spacer is substantially cylindrical and expands substantially symmetrically.
 25. A radially expandable pipe as claimed in claim 23 in which the spacer is substantially cylindrical and has elements that are designed to expand asymmetrically about the center of the pipe.
 26. A radially expandable pipe as claimed in claim 23 having a plurality of spacers positioned along the length and/or around the circumference of the radially expandable pipe such that when the pipe is expanded they expand to different radial lengths to hold the curved pipe in place within the well bore. 